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The Silicon Labs Community will be migrating storage resource provider infrastructure and data to a new data center. It will cause some read-only time on the community during the migration. As a community member, you will be able to read content but your write operations will be disabled during the maintenance window.

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This article describes what is the role of each of the advertising sets that are used by the Bluetooth Mesh stack. The advertising sets are briefly documented on the source code comments of the Bluetooth Mesh SDK examples, see following snippet from main.c:

// Bluetooth advertisement set configuration
//
// At minimum the following is required:
// * One advertisement set for Bluetooth LE stack (handle number 0)
// * One advertisement set for Mesh data (handle number 1)
// * One advertisement set for Mesh unprovisioned beacons (handle number 2)
// * One advertisement set for Mesh unprovisioned URI (handle number 3)
// * N advertisement sets for Mesh GATT service advertisements
// (one for each network key, handle numbers 4 .. N+3)
//
#define MAX_ADVERTISERS (4 + MESH_CFG_MAX_NETKEYS)

Here is a more verbose explanation for each set:

handle 0 - Bluetooth LE stack

This advertising set is reserved for "normal" BLE operation. For example, if user application starts advertising using command gecko_cmd_le_gap_set_mode (deprecated), then advertising set 0 is used. The mesh stack does not use this advertising set at all, it is reserved for user application.

handle 1 - Mesh data

This set is used for BLE Mesh data traffic. The stack is in control of the advertising data and the advertising parameters for this set, and the user application must not override the parameters or use this set for anything else.

handle 2 - Mesh unprovisioned beacons

This set is used for unprovisioned beacons (PB-ADV) by the mesh stack. The data advertised using this set is generated by the mesh stack, but the advertising parameters can be modified by the user application to control the cadence used in unprovisioned beacon advertising.

handle 3 - Mesh unprovisioned URI

Used only in case the device supports OOB data retrieval over URI. In that case, this set is used to advertise the URI (interleaved with the unprovisioned beacons). As with the unprovisioned beacons set, the stack generates the data to be advertised, but the user application is free to set the parameters controlling the advertising cadence.

handle 4 - Mesh GATT service advertisements

This handle is used for Mesh GATT service advertisements. If device is unprovisioned, then this handle is used for unprovisioned beacons (PB-GATT). For provisioned devices this handle is used for advertising the proxy service (if enabled).

Further reading

Following article shows how to start your own BLE advertisements in a BLE mesh application:

• Adding custom advertising to the Bluetooth mesh examples

Introduction

One of the new features added in Bluetooth 5 is the LE coded PHY which enables longer range connections. This article describes how advertising on the coded PHY works, as well how to establish a connection using the coded PHY.

Discussion

Traditional Bluetooth low energy advertisements use channels 37, 38 and 39 only for advertising. The advertisement is identical on each channel and contains the advertiser’s address and advertising data payload. Starting in Bluetooth 5 it is possible to offload the advertising data payload onto one of the data channels. In this new type of advertisement, the same three advertising channels are used but instead of including the data payload, they include a pointer to the data channel and the offset time until the data payload is expected. This type of advertising is known as extended advertising. The following diagram is provided to illustrate

The common extended advertising format looks like this

The ADV mode field is shown below, note that is not permitted to be scannable and connectable at the same time

The extended header is laid out as follows, not all fields will be present in every advertisement

The aux pointer field provides information about the auxiliary advertisement as shown below

The channel index indicates which channel the auxiliary advertisement will come on. The CA field indicates the clock accuracy, the offset units indicate whether the offset (time until the auxiliary advertisement) is in units of 30 us or 300 us, the aux offset indicates the number of offset units until the auxiliary advertisement can be expected and the aux PHY indicates which PHY be used in the auxiliary advertisement.

The sync info field is not presently used. The Tx Power field indicates the transmitted power in dBm.

Another feature of these extended advertisements is that it is possible to specify the PHY used for the primary and secondary advertisements separately. To set the PHY used for advertisments, the following API function can be used

gecko_cmd_le_gap_set_advertise_phy(0, le_gap_phy_coded , le_gap_phy_coded);

The parameters indicate the advertisement set to be used, the PHY for primary advertisements and the PHY used for secondary advertisements

Advertisements on the coded PHY do not support active scanning. This means that is always necessary to use the new connectability mode le_gap_connectable_non_scannable.

To start advertising, the following API function can be used

gecko_cmd_le_gap_start_advertising(0,le_gap_general_discoverable, le_gap_connectable_non_scannable);

Remaining advertising parameters can be set as they would with the traditional 1 Mbps PHY.

Please refer here for an article summarizing the changes to the API in version 2.8.

Example Applications

Source code for an example advertiser and observer are attached below. To use this code please do as follows

1. Create an soc-empty sample application from the project menu->new->Silicon Labs Appbuilder
2. Save app.c and app.h for the advertiser to the project folder
3. Comment out the while(1) in main.c
4. add a call to appMain() just before the while(1) loop
5. add the following line near the top of main.c

#include “app.h”

1. Build the project and flash to your radio board.
2. Create a second soc-empty sample as in #1 above for the client.
3. Save app.c and app.h for the client to this project folder (note that the contents of app.c are different)
4. Repeat steps 3 – 5 for this project.
5. Open hal-config.h and change the definition of HAL_VCOM_ENABLE to 1
6. Go to the hardware\kit\common\drivers folder of your SDK and copy retargetio.c, retargetserialc and retargetserial.h to the hardware\kit\common\drivers in the project
7. Build and flash to a second radio board.
8. Launch a console for this second board , select the Serial1 tab and hit enter in the text box at the bottom to wake it up.
9. Press reset on the WSTK to see the startup messages.
10. Power up the first WSTK and you’ll see that the client connects to it on the LE coded PHY.

While developing with Silicon Labs Bluetooth SDK, users can use the API – gecko_cmd_le_gap_bt5_set_adv_data() to set the advertisement and scan response data. The data has a standard format, whereas the data passed to above API is uint8array.  This article will focus on adding a middle layer between user application and the BG stack API to set the advertisement payload, which makes the payload more straightforward, visible and easier to understand for users.

For more information about the advertising data, you can go to the Bluetooth KBA Index and see the “Advertising” category.